You get given money daily by the king, and when you get your pro debut, you'll get millions of dollars daily. Then everyday in generation two and so on, you'll get money from your parent/s.
You can also get money from doing part time jobs, which is when you're an adult. you go to those by going to away, and pressing the 1st button instead of the 2nd when you see the music practise. by doing this you can select to work at a cake or fruit shop. argh, my first gen didn't even become a music star, it was so hard to make money. >.>